1. Field of the Invention
The present invention concerns a method of providing on a glass surface a hydrophobic coating comprising a suitably treated chitosan biopolymer, and the resulting coated glass article.
2. Related Art
The desirability of providing a hydrophobic surface to windshields has driven the sales of products, usually silicone-based, which, when applied to the surface of a windshield or other glass, create a hydrophobic film that causes water to run off the glass. A drawback of such products is that they are soon worn away by weather and the action of windshield wipers and have to be re-applied at frequent intervals. Under conditions of heavy use in protracted bad weather, e.g., rain, sleet and snow, reapplication every three to four weeks or at even shorter intervals may be required. Further, the application of silicone spray products can cause “star” effects from lights during nighttime driving. Such star effects are believed to be the result of streaks in the applied coating resulting from uneven application or improper or incomplete buffing of the applied coating.
There are various known methods for treating a glass surface to enable the bonding to it of different types of surface coatings. Various methods are described in the article Glass Surfaces: Old, New and Engineered by Carlo G. Pantano (Department of Materials Science and Engineering, Materials Research Institute, University Park, Pa. 16802), the disclosure of which is incorporated by reference herein. Specific coatings applied to such treated glass include anti-reflective coatings and dichroics for cameras; low-emissivity coatings for energy-saving windows; coatings for scratch resistance; liquid-crystal coatings for display screens, etc.
Among coatings for self-cleaning glass surfaces is a hydrophilic coating of the anatase form of titanium dioxide which has been treated with ultraviolet light. Such coatings are actively involved in chemical reactions that break down organic material deposited on the coated glass surface and the coating's hydrophilic characteristics are said to cause water not to collect in beads but rather to sheet on the surface, thereby facilitating rapid, reduced-spotting evaporation of the water.
U.S. Pat. No. 7,288,532, issued Oct. 30, 2007 to Gregory F. Payne et al., and entitled “Modified Chitosan Polymers And Enzymatic Methods For The Production Thereof”, discloses that enzymatic reactions may be employed to modify the chitosan in order to render it hydrophobic. The disclosure of U.S. Pat. No. 7,288,532 is incorporated by reference herein.
As used herein and in the claims, the word “durable” as applied to describe the hydrophobic coating applied to the surface of an article in accordance with the present invention, means a coating which may last for the entire useful life of the article, i.e., a coating which is “substantially permanent”, or a coating which is not worn away in normal use over a period of years, e.g., at least one year of normal use of the article, such as the normal use of windshields or other glass articles. For such glass articles the coating is usually “substantially permanent”.